Positive active material, lithium battery including the same, and method of manufacturing the positive active material

ABSTRACT

A positive active material including a core including a compound capable of reversibly intercalating and deintercalating lithium and LiNaSO 4  that is coated on at least a part of a surface of the core or that blends with the core.

CROSS-REFERENCE TO RELATED APPLICATION

Korean Patent Application No. 10-2015-0184126, filed on Dec. 22, 2015,in the Korean Intellectual Property Office, and entitled: “PositiveActive Material, Lithium Battery Including the Same, and Method ofManufacturing the Positive Active Material,” is incorporated byreference herein in its entirety.

BACKGROUND

1. Field

Embodiments relate to a positive active material, a lithium batteryincluding the positive active material, and a method of manufacturingthe positive active material.

2. Description of the Related Art

With the development of small high-tech devices such as digital cameras,mobile devices, laptops, and computers, the demand for a lithiumsecondary battery as an energy source has rapidly increased. Inaddition, with the spread of the use of a lithium secondary battery fromportable information electronic devices to the industries of electrictools or vehicles, the demand for a lithium secondary battery with highcapacity, high output, and safety has further increased.

SUMMARY

Embodiments are directed to a positive active material including a coreincluding a compound capable of reversibly intercalating anddeintercalating lithium and LiNaSO₄ that is coated on at least a part ofa surface of the core or that blends with the core.

The LiNaSO₄ may be attached on the core in a layered form or an islandform.

An amount of the core may be in a range of about 95 wt % to about 99.5wt %.

An amount of the LiNaSO₄ may be in a range of about 0.5 wt % to about 5wt %, of a total weight of the core and the LiNaSO₄.

An amount of the core may be in a range of about 97 wt % to about 99.3wt % of a total weight of the core and the LiNaSO₄. An amount of theLiNaSO₄ may be in a range of about 0.7 wt % to about 3 wt % of a totalweight of the core and the LiNaSO₄.

The core may include at least one selected from compounds represented by

Formulae 1 to 3:

Li_(a)(Ni_(x)M′_(y))O₂   [Formula 1]

wherein, in Formula 1, M′ is at least one element selected from Co, Mn,Fe, V, Cu, Cr, Al, Mg, and Ti; and 0.9<a≦1.1, 0≦<x<0.4, 0.6≦y≦1, andx+y=1,

LiMPO₄   [Formula 2]

wherein, in Formula 2, M is at least one element selected from Fe, Mn,Ni, Co, and V,

Li_(1+y)Mn_(2−y−z)M_(z)O_(4−x)Q_(x)   [Formula 3]

wherein, in Formula 3, M is at least one element selected from Mg, Al,Ni, Co Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr, and Zn; Q isat least one element selected from N F, S, and Cl; and 0≦x≦1, 0≦y≦0.34,and 0≦z≦1,

The core may include the compound represented by Formula 1. The compoundrepresented by Formula 1 may be further substituted or doped with atleast one element selected from Ca, Mg, Al, Ti, Sr, Fe, Co, Cu, Zn, Y,Zr, Nb, and B, wherein the substituted or doped one element is differentfrom Ni and M′.

Embodiments are also directed to a lithium battery including a positiveelectrode including the positive active material as described above, anegative electrode facing the positive electrode, and an electrolytebetween the positive electrode and the negative electrode.

The lithium battery may operate within a voltage range of about 4.3 V toabout 4.6 V.

Embodiments are also directed to a method of manufacturing a positiveactive material including preparing a compound capable of reversiblyintercalating and deintercalating lithium, adding and mixing a sodiumsource and a sulfate source to the compound to obtain a powder mixture,and heat-treating the powder mixture to obtain a positive activematerial including LiNaSO₄ that is coated on at least a part of asurface of the compound capable of reversibly intercalating anddeintercalating lithium or that blends with the compound capable ofreversibly intercalating and deintercalating lithium.

The sodium source may include at least one selected from sodium dodecylsulfate (CH₃(CH₂)₁₁SO₄Na), sodium sulfate (Na₂SO₄), sodium nitrate(NaNO₃), sodium acetate (CH₃COONa), sodium carbonate (Na₂CO₃), sodiumbicarbonate (NaHCO₃), and sodium hydroxide (NaOH).

The sulfate source may include at least one selected from sodium dodecylsulfate (CH₃(CH₂)₁₁SO₄Na), sodium sulfate (Na₂SO₄), sulfuric acid(H₂SO₄), ammonium sulfate ((NH₄)₂SO₄), and lithium sulfate (Li₂SO₄).

The heat-treating may be performed at a temperature in a range of about600° C. to about 1,000° C.

An amount of the compound capable of intercalating and deintercalatinglithium may be in a range of about 95 wt % to about 99.5 wt % of a totalweight of the compound capable of intercalating and deintercalatinglithium and the LiNaSO₄. An amount of the LiNaSO₄ may be in a range ofabout 0.5 wt % to about 5 wt %, of the total weight of the compoundcapable of intercalating and deintercalating lithium and the LiNaSO₄.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates a cutaway and partially exploded schematic view of astructure of a lithium battery according to an embodiment;

FIG. 2A illustrates the results of an XRD analysis performed on apositive active material prepared in Example 1, and FIG. 2B illustratesan enlarged portion of 20° to 35° 2θ taken from the graph shown in FIG.2A showing the presence of a LiNaSO₄ phase; and

FIG. 3 illustrates the measured results of capacity retention ratios(CRR) per cycle of lithium batteries prepared in Examples 1 to 4 andComparative Examples 1 and 2.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art.

According to an embodiment, a positive active material may include acore including a compound capable of reversibly intercalating anddeintercalating lithium, and LiNaSO₄ coated on or blended with the core.

The core may be a suitable compound that is capable of reversiblyintercalating and deintercalating lithium. For example, the compound maybe represented by Li_(a)A_(1−b)X_(b)D₂ (where 0.90≦a≦1.8 and 0≦b≦0.5);Li_(a)A_(1−b)X_(b)O_(2−c)D_(c) (where 0.90≦a≦1.8, 0≦b≦0.5, and0≦c≦0.05); LiE_(2−b)X_(b)O_(4−c)D, (where 0≦b≦0.5 and 0≦c≦0.05);Li_(a)Ni_(1−b−c)Co_(b)X_(c)D_(α)(where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05,and 0<α≦2); Li_(a)Ni_(1−b−c)Co_(b)X_(c)O_(2−α)T_(α) (where 0.90≦a≦1.8,0≦b≦0.5, 0≦c≦0.05, and 0<α≦2); Li_(a)Ni_(1−b−c)Co_(b)X_(c)O_(2−α)T₂(0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<a<2);Li_(a)Ni_(1−b−c)Mn_(b)X_(c)D_(α)(where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05,and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)X_(c)O_(2−α)T_(α)(where 0.90<a≦1.8,0≦b≦0.5, 0≦c≦0.05, and 0<α<2); Li_(a)Ni_(1−b−c)Mn_(b)X_(c)O_(2−α)T₂(where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, and 0<α<2);Li_(a)Ni_(b)E_(c)G_(d)O₂ (where 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, and0.001≦d≦0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (0.90≦a≦1.8, 0≦b≦0.9,0≦c≦0.5, 0≦d≦0.5, and 0.001≦e≦0.1); Li₁NiG_(b)O₂ (where 0.90≦a≦1.8 and0.001≦b≦0.1); Li_(a)CoG_(b)O₂ (where 0.90≦a ≦1.8 and 0.001≦b≦0.1);Li_(a)MnG_(b)O₂ (where 0.90≦a≦1.8 and 0.001≦b≦0.1); Li_(a)Mn₂G_(b)O₄(where 0.90≦a≦1.8 and 0.001≦b≦0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅;LiZO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (where 0≦f≦2); Li_(3−f))Fe₂(PO₄)₃(where 0≦f ≦2); or LiFePO₄.

In the above formulas, A is selected from Ni, Co, Mn, and a combinationthereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rareearth element, and a combination thereof; D is selected from 0, F, S, P,and a combination thereof; E is selected from Co, Mn, and a combinationthereof; T is selected from F, S, P, and a combination thereof; G isselected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and a combinationthereof; Q is selected from Ti, Mo, Mn, and a combination thereof; Z isselected from Cr, V, Fe, Sc, Y, and a combination thereof; and J isselected from V, Cr, Mn, Co, Ni, Cu, and a combination thereof.

In an embodiment, the core may include at least one of compoundsrepresented by Formulae 1 to 3:

Li_(a)(Ni_(x)M′_(y))O₂   [Formula 1]

In Formula 1, M′ is at least one element selected from Co, Mn, Fe, V,Cu, Cr,

Al, Mg, and Ti; and 0.9<a≦1.1, 0≦x<0.4, 0.6≦y≦1, and x+y=1

LiMPO₄   [Formula 2]

In Formula 2, M is at least one element selected from Fe, Mn, Ni, Co,and V

Li_(1+y)Mn_(2−y−z)M_(z)O_(4−x)Q_(x)   [Formula 3]

In Formula 3, M is at least one element selected from Mg, Al, Ni, Co,Fe, Cr, Cu, B, Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr, and Zn, Q is atleast one element selected from N, F, S, and Cl, and 0≦x≦1, 0≦y≦0.34,and 0≦z≦1.

The compound represented by Formula 1 may be further substituted ordoped with at least one element selected from Ca, Mg, Al, Ti, Sr, Fe,Co, Cu, Zn, Y, Zr, Nb, and B, wherein the substituted or doped elementis different from Ni and M′.

The core may be in a form of a one-body particle. Herein, the term“one-body particle” indicates a particle that is different from anagglomerate in which small particles are clustered together. Theone-body particle may be formed of one particle that exists alonewithout having a grain boundary in the particle. The specific surfacearea of the core formed of the one-body particle may be less than a coreformed from an aggregate. The core in the form of a one-body particlemay suppress side reactions with an electrolyte.

In some implementations, the core may be a secondary particle that isformed by agglomerating primary particles. The secondary particle mayinclude gaps and boundaries between the primary particles. The secondaryparticle may provide high capacity due to an increase in a specificsurface area.

The core may have a suitable average particle diameter. For example,when the average particle diameter of the core is not too small,excessive reactivity with an electrolyte solution that may deterioratecycle characteristics may be avoided. When the average particle diameterof the core is not too large, a deterioration of dispersion stability inthe formation of a positive electrode slurry may be avoided, and a roughsurface of a positive electrode may be avoided. An average particlediameter D50 of the core may be about 50 μm or less, or, for example, ina range of about 1 μm to about 30 μm, or, for example, about 5 μm toabout 25 μm, or, for example, about 10 μm to about 20 μm.

As used herein, the term “average particle diameter (D50)” refers to acumulative average particle diameter that corresponds to 50 vol % in acumulative distribution curve of a particle diameter having the totalvolume as 100%. The average particle diameter (D50) may be measured byusing a method known in the art. An example of the method may includemeasuring by a particle size analyzer or measuring from a TEM or SEMimage. In some embodiments, the method may include measuring with ameter by dynamic light-scattering, performing data analysis to count thenumber of particles with respect to each size range, and obtaining D50from the resulting calculation.

The positive active material may be prepared by coating LiNaSO₄ onto atleast a part of a surface of the core including the compound capable ofreversibly intercalating or deintercalating lithium or by blending thecore with LiNaSO₄.

LiNaSO₄ may facilitate the conduction of lithium ions, may help suppressa reaction between a positive active material core capable ofintercalating or deintercalating lithium ions and an electrolytesolution, and may help improve lifespan characteristics of the lithiumbattery.

The LiNaSO₄ may be formed, for example, when a sodium source and asulfate source react with a lithium source that is present in thecompound capable of reversibly intercalating and deintercalatinglithium. Thus, the LiNaSO₄ may be coated on or blend with a surface ofthe compound capable of reversibly intercalating and deintercalatinglithium.

In one embodiment, the LiNaSO₄ may be coated onto a surface of the core.The LiNaSO₄ may be coated in a layered structure or in an island shape.Herein, the term “island shape” refers to a shape that isdiscontinuously attached to the surface of the core. For example, anisland shape may be a semispherical, non-spherical, or irregular shapehaving a volume.

In the positive active material, an amount of the core may be in a rangeof about 95 wt % to about 99.5 wt % of a total weight of the core andthe LiNaSO₄, and an amount of the LiNaSO₄ may be in a range of about 0.5wt % to about 5 wt % of the total weight of the core and the LiNaSO₄.For example, in the positive active material, an amount of the core maybe in a range of about 97 wt % to about 99.3 wt % of the total weight ofthe core and the LiNaSO₄, and an amount of the LiNaSO₄ may be in a rangeof about 0.7 wt % to about 3 wt % of the total weight of the core andthe LiNaSO₄. When the amounts of the core and the LiNaSO₄ are withinthese ranges, side reactions between the core and an electrolyte may beeffectively suppressed and lifespan characteristics of a lithium batterymay be improved.

The positive active material according to an embodiment may be used inthe manufacture of a lithium battery having excellent cyclecharacteristics by coating or blending of LiNaSO₄, which has lithium ionconductivity.

According to an embodiment, a method of manufacturing a positive activematerial is provided.

The method of manufacturing a positive active material may includepreparing a compound capable of reversibly intercalating anddeintercalating lithium, adding and mixing a sodium source and a sulfatesource to the compound to obtain a powder mixture, and heat-treating thepowder mixture to obtain a positive active material that is coated on orblends with at least a part of a surface of the compound capable ofreversibly intercalating and deintercalating lithium.

The compound capable of reversibly intercalating and deintercalatinglithium is the same as defined in the description above. The compoundmay be at least one selected from compounds provided as examples.

A suitable solvent may be used in the solution. Examples of the solventinclude water, ethanol, hexane, a heptane, isopropanol, andN-methylpyrrolidone (NMP).

The sodium source and the sulfate source are raw materials that may beused to form LiNaSO₄. The sodium source and the sulfate source may reactwith an excessive amount of lithium existing on a surface of thecompound capable of reversibly intercalating and deintercalating lithiumto form LiNaSO₄.

The sodium source may be a salt including sodium (Na). Examples of thesodium source may include sodium dodecyl sulfate (CH₃(CH₂)₁₁SO₄Na),sodium sulfate (Na₂SO₄), sodium nitrate (NaNO₃), sodium acetate(CH₃COONa), sodium carbonate (Na₂CO₃), sodium hydrogen carbonate(NaHCO₃), and sodium hydroxide (NaOH). At least one selected therefrommay be used.

Examples of the sulfate source may include sodium dodecyl sulfate(CH₃(CH₂)₁₁SO₄Na), sodium sulfate (Na₂SO₄), sulfuric acid (H₂SO₄),ammonium sulfate ((NH₄)₂SO₄), and lithium sulfate (Li₂SO₄). At least oneselected therefrom may be used.

In an implementation, compounds such as sodium dodecyl sulfate andsodium sulfate may serve as both the sodium source and the sulfatesource.

The sodium source and the sulfate source may be added in desired amountsby taking into account a stoichiometry ratio in a solution including thecompound capable of reversibly intercalating and deintercalatinglithium.

The mixed solution may be heat-treated to obtain a positive activematerial having LiNaSO₄ that is coated on at least a part of a surfaceof the compound capable of reversibly intercalating and deintercalatinglithium or that blends with the compound capable of reversiblyintercalating and deintercalating lithium.

The heat-treating process may be performed in air at a temperature in arange of about 600° C. to about 1,000° C. For example, the heat-treatingprocess may be performed at a temperature in a range of about 700° C. toabout 900° C. for about 4 hours to about 20 hours.

Before heat-treating the mixed solution, the method may further includeevaporating the solvent from the mixed solution. When the solvent isevaporated from the mixed solution, a gel may be obtained. The gel maybe heat-treated to obtain a positive active material that is coated orblended with LiNaSO₄.

A lithium battery may include a positive electrode including thepositive active material, a negative electrode facing the positiveelectrode, and an electrolyte between the positive electrode and thenegative electrode.

The positive electrode includes the positive active material. Thepositive electrode may be manufactured by, for example, mixing thepositive active material, a conducting agent, and a binder in a solventto prepare a positive active material composition, and molding thepositive active material composition to have a predetermined shape or bycoating a current collector such as a copper foil with the positiveactive material composition.

The conducting agent included in the positive active materialcomposition may increase an electrical conductivity by providing aconduction pathway to the positive active material. Examples of theconducting agent may include a carbon-based material such as carbonblack, acetylene black, Ketjen black, or carbon fiber (e.g., vaporgrowth carbon fiber); a metal-based material such as a metal powder ormetal fiber of copper, nickel, aluminum, or silver; a conductive polymersuch as a polyphenylene derivative; or a conducting material including amixture thereof. An amount of the conducting agent may be appropriatelycontrolled. For example, a weight ratio of the positive active materialand the conducting agent may be in a range of about 99:1 to about 90:10.

The binder included in the positive active material compositioncontributes in binding of the positive active material and theconducting agent and binding of the positive active material to thecurrent collector. An amount of the binder may be in a range of about 1part to about 50 parts by weight based on 100 parts by weight of thepositive active material. For example, an amount of the binder may be ina range of about 1 part to about 30 parts by weight, for example, about1 part to about 20 parts by weight, or about 1 part to about 15 parts byweight, based on 100 parts by weight of the positive active material.Examples of the binder may include polymers such as polyvinylidenefluoride (PVdF), polyvinylidene chloride, polybenzimidazole, polyimide,polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol,carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, reproducedcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene,polypropylene, polystyrene, polymethyl methacrylate, polyaniline,acrylonitrile butadiene styrene, phenol resin, epoxy resin, polyethyleneterephthalate, polytetrafluoroethylene, polyphenyl sulfide,polyamideimide, polyetherimide, polyethylene sulfone, polyamide,polyacetal, polyphenylene oxide, polybutylene terephthalate,ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrenebutadiene rubber (SBR), fluorine rubber, or a combination thereof

Examples of the solvent may include NMP, acetone, or water. An amount ofthe solvent may be in a range of about 1 part to about 100 parts byweight based on 100 parts by weight of the positive active material.When the amount of the solvent is within this range, an active materiallayer may be easily formed.

A thickness of the current collector may be in a range of about 3 μm toabout 500 μm. A current collectors that does not cause a chemical changeto a battery and has high conductivity may be used. Examples of thecurrent collector for a positive electrode may include stainless steel,aluminum, nickel, titanium, calcined carbon, and copper and stainlesssteel that are surface-treated with carbon, nickel, titanium, or silver.The current collector for a positive electrode may have an uneven microstructure at its surface to enhance a binding force with the positiveactive material. The current collector may be in various forms includinga film, a sheet, a foil, a net, a porous body, a foaming body, or anon-woven body.

The positive active material composition may be directly coated onto acurrent collector. In some implementations, the positive active materialcomposition may be cast onto a separate support to form a positiveactive material film, which may then be separated from the support andlaminated on a copper foil current collector to prepare a positiveelectrode plate.

The positive active material composition may be printed onto a flexibleelectrode substrate to manufacture a printable battery, in addition tothe use in manufacturing a lithium battery.

For the manufacture of a negative electrode, a negative active materialcomposition may be prepared by mixing a negative active material, abinder, a solvent, and, optionally, a conducting agent.

Examples of the negative active material may include lithium metal, ametal that is alloyable with lithium, a transition metal oxide. acompound capable of doping and de-doping lithium, and a compound capableof reversibly intercalating and deintercalating lithium ions.

Examples of the transition metal oxide may include a tungsten oxide, amolybdenum oxide, a titanium oxide, a lithium titanium oxide, a vanadiumoxide, and a lithium vanadium oxide.

Examples of the compound capable of doping and de-doping lithium mayinclude Si; SiO_(x) (where 0<x<2); a Si-Y′ alloy (where Y′ is an alkalimetal, an alkali earth metal, a Group 13 element, a Group 14 element, aGroup 15 element, a Group 16 element, a transition metal, a rare-earthelement, or a combination thereof, but not Si); Sn; SnO₂; and a Sn—Y″alloy (where Y″ is an alkali metal, an alkali earth metal, a Group 13element, a Group 14 element, a Group 15 element, a Group 16 element, atransition metal, a rare-earth element, or a combination thereof, butnot Sn). Also, at least one of the materials capable of doping andde-doping lithium may be used in combination with SiO₂. The element Y′or Y″ may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db,Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag,Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, ora combination thereof.

The compound capable of reversibly intercalating and deintercalatinglithium ions may be any one of various carbon-based materials that aregenerally used in a lithium battery. Examples of the compound capable ofreversibly intercalating and deintercalating lithium ions may includecrystalline carbon, amorphous carbon, and a mixture thereof. Examples ofthe crystalline carbon may include natural graphite and artificialgraphite, each of which may have an amorphous shape, a plate shape, aflake shape, a spherical shape, or a fiber shape. Examples of theamorphous carbon may include soft carbon (low-temperature calcinedcarbon), hard carbon, meso-phase pitch carbide, and calcined cokes.

The conducting agent, the binder, and the solvent included in preparingthe negative active material composition may be the same as thoseincluded in the positive active material composition. In someimplementations, a plasticizer may be further added to the positiveactive material composition and to the negative active materialcomposition in order to form pores in a corresponding electrode plate.Amounts of the negative active material, the conducting agent, thebinder, and the solvent may be at the same levels used in a conventionallithium battery.

A negative electrode current collector may have a thickness of about 3μm to about 500 μm. A current collectors that does not cause a chemicalchange to a battery and has high conductivity may be used as thenegative electrode current collector. Examples of the current collectorfor a negative electrode may include stainless steel, aluminum, nickel,titanium, calcined carbon, and aluminum and stainless steel that aresurface-treated with carbon, nickel, titanium, or silver. The currentcollector for a negative electrode may have an uneven micro structure atits surface to enhance a binding force with the negative activematerial. The current collector may be used in various forms including afilm, a sheet, a foil, a net, a porous body, a foaming body, a non-wovenbody.

The negative active material thus prepared may be directly coated ontothe current collector for a negative electrode to form a negativeelectrode plate, or may be cast onto a separate support, and a negativeactive material film separated from the support may be laminated ontothe current collector for a negative electrode.

The positive electrode and the negative electrode may be separated by asuitable separator for use in a lithium battery. The separator mayinclude a material that has a low resistance to the migration of ions ofan electrolyte and an excellent electrolytic solution-retainingcapability. For example, the separator may include a material selectedfrom glass fiber, polyester, Teflon, polyethylene, polypropylene,polytetrafluoroethylene (PTFE), and a combination thereof, each of whichmay be non-woven or woven. The separator may have a pore diameter in arange of about 0.01 μm to about 10 μm, and a thickness in a range ofabout 5 μm to about 300 μm.

A lithium salt-containing non-aqueous based electrolyte solution mayinclude a non-aqueous electrolyte and a lithium salt. Examples of thenon-aqueous electrolyte may include a non-aqueous electrolyte solution,a solid electrolyte, and an inorganic solid electrolyte.

The non-aqueous electrolyte solution may be a non-aprotic organicsolvent.

Examples of the non-aprotic organic solvent may includeN-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate,butylene carbonate, dimethyl carbonate, diethyl carbonate,gamma-butyrolactone, 1,2-dimethoxy ethane, tetrahydrofuran,2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide,dimethylformamide. dioxolane, acetonitrile. nitromethane, methylformate, methyl acetate, phosphoric acid triester. trimethoxymethane,dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate, and ethylpropionate.

Examples of the organic solid electrolyte may include polyethylenederivatives, polyethylene oxide derivatives, polypropylene oxidederivatives, phosphoric acid ester polymers, polyagitation lysine,polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, andpolymers containing ionic dissociation groups.

Examples of the inorganic solid electrolyte may include nitrides,halides, and sulfates of lithium such as Li₃N, LiI, Li₅NI₂,Li₃N—LiI-LiOH, LiSiO₄, LiSiO₄—LiI-LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, and Li₃PO₄—Li₂S—SiS₂.

The lithium salt may be a suitable lithium salt for use in a lithiumbattery and that is soluble in the lithium salt-containing non-aqueouselectrolyte. For example, the lithium salt may include at least oneselected from LiCl, LiBr, LiI, LiClO₄, LiBF₄,

LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithiumcarbonate, lithium tetraphenyl borate, and lithium imide.

Lithium batteries may be classified as lithium ion batteries, lithiumion polymer batteries, and lithium polymer batteries according to thetype of separator and electrolyte used therein. In addition, lithiumbatteries may be classified as a cylindrical type, a rectangular type, acoin type, and a pouch type according to a battery shape, and may alsobe classified as a bulk type and a thin type according to a batterysize. Lithium batteries may be also used either as primary lithiumbatteries or secondary lithium batteries.

FIG. 1 illustrates a cutaway and partially exploded schematic view of atypical structure of a lithium battery 30 according to an embodiment.

Referring to FIG. 1, the lithium battery 30 may include a positiveelectrode 23, a negative electrode 22, and a separator 24 between thepositive electrode 23 and the negative electrode 22. The positiveelectrode 23, the negative electrode 22, and the separator 24 may bewound or folded, and then accommodated in a battery case 25.Subsequently, an electrolyte may be injected into the battery case 25,and the battery case 25 may be sealed by a sealing member 26, therebycompleting the manufacture of the lithium battery 30. The battery case25 may have a cylindrical shape, a rectangular shape, or a thin-filmshape. The lithium battery 30 may be a lithium ion battery.

The lithium battery may be used as a power source for small-sizeddevices such as mobile phones or portable computers, or as a unitbattery of a battery module including a plurality of batteries for usein a medium-to-large-sized device.

Examples of the medium-to-large-sized device may include a power tool;an xEV such as an electric vehicle (EV), a hybrid electric vehicle(HEV), and a plug-in hybrid electric vehicle; an electric bicycle suchas E-bike or E-scooter; an electric golf cart; an electric truck; anelectric commercial vehicle; or an electric power storage system. Thelithium battery may be suitable for a use that requires a high output. ahigh voltage. and high temperature operability. The lithium battery maybe used in applications that require a high voltage range of about 4.3 Vto about 4.6 V.

The following Examples and Comparative Examples are provided in order tohighlight characteristics of one or more embodiments, but it will beunderstood that the Examples and Comparative Examples are not to beconstrued as limiting the scope of the embodiments, nor are theComparative Examples to be construed as being outside the scope of theembodiments. Further, it will be understood that the embodiments are notlimited to the particular details described in the Examples andComparative Examples.

EXAMPLE 1

(1) Preparation of Positive Active Material

LiCoO₂ to be used as a core of a positive active material was preparedas follows.

First, Li₂CO₃ and Co₃O₄ were mixed so that a molar ratio of Li:Co was1.03:1.The mixture was calcined at 1,000° C. in an air atmosphere for 10hours to obtain LiCoO₂. The calcined LiCoO₂ was pulverized andclassified using a sieve to prepare a LiCoO₂ powder having an averageparticle diameter of about 15 μm.

In order to coat LiNaSO₄ on the LiCoO₂ powder, 0.5 g of Na₂SO₄ was addedto 100 g of the LiCoO₂ powder and mixed to prepare a powder mixture.

The powder mixture thus obtained was heat-treated at 800° C. in an airatmosphere for 10 hours to obtain a positive active material having 0.5wt % of LiNaSO₄ coated on a surface of LiCoO₂.

(2) Preparation of Lithium Battery

94 wt % of the positive active material prepared as described above. 3wt % of carbon black. as a conducting agent, and 3 wt % of PVDF, as abinder, were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare apositive electrode slurry. The positive electrode slurry was coated ontoan aluminum (Al) foil having a thickness in a range of about 20 μm toabout 30 μm, to serve as a positive electrode current collector, and thecoated positive electrode slurry was dried. The resultant wasroll-pressed to prepare a positive electrode.

Lithium metal was used as a counter electrode (a negative electrode) ofthe positive electrode. An electrolyte was prepared by adding 1.1 MLiPF₆ to a solvent. The solvent was prepared by mixing ethylenecarbonate (EC), ethylmethyl carbonate (EMC), and dimethyl carbonate(DMC) at a volume ratio of 3:5:2.

A separator formed of a porous polyethylene (PE) film was disposedbetween the positive electrode and the negative electrode to form abattery assembly. The battery assembly was rolled and pressed to beaccommodated in a battery case. Then, the electrolyte was injected intothe battery case to prepare a lithium battery (a coin half cell, 2016type).

EXAMPLE 2

A positive active material and a lithium battery were prepared in thesame manner as in Example 1, except that a positive active materialhaving 0.7 wt % of LiNaSO₄ coated on a surface of LiCoO₂ was prepared byadding and mixing 0.7 g of Na₂SO₄ to 100 g of a LiCoO₂ powder andheat-treating the mixture.

EXAMPLE 3

A positive active material and a lithium battery were prepared in thesame manner as in Example 1, except that the positive active materialhaving 1.5 wt % of LiNaSO₄ coated on a surface of LiCoO₂ was prepared byadding and mixing 1.5 g of Na₂SO₄ to 100 g of a LiCoO₂ powder andheat-treating the mixture.

EXAMPLE 4

A positive active material and a lithium battery were prepared in thesame manner as in Example 1, except that the positive active materialhaving 2.9 wt % of LiNaSO₄ coated on a surface of LiCoO₂ was prepared byadding and mixing 2.9 g of Na₂SO₄ to 100 g of a LiCoO₂ powder andheat-treating the mixture.

COMPARATIVE EXAMPLE 1

A lithium battery was prepared in the same manner as in Example 1,except that the LiCoO₂ powder prepared in Example 1 itself without acoating process was used as a positive active material.

COMPARATIVE EXAMPLE 2

A positive active material and a lithium battery were prepared in thesame manner as in Example 1, except that the positive active materialhaving 0.2 wt % of LiNaSO₄ coated on a surface of LiCoO₂ was prepared byadding and mixing 0.2 g of Na₂SO₄ to 100 g of a LiCoO₂ powder andheat-treating the mixture.

Evaluation Example 1: X-ray Diffraction (XRD) Analysis of LiNaSO₄

XRD analysis using an X-ray diffractometer (X'pert PRO MPD, availablefrom PANalytical) was performed on the positive active material preparedin Example 1, and the results of the analysis are shown in FIGS. 2A and2B. The analysis conditions included a CuK-alpha characteristic X-raywavelength of 1.541 Å.

As shown in FIG. 2A, the positive active material prepared in Example 1mainly showed an LCO phase. FIG. 2B is an enlarged view of a portion of20° to 35° 2θ in the XRD graph of FIG. 2A, where a particular peakrepresenting a LiNaSO₄ phase was evident within a range of 20° to 35°.Thus, it may be confirmed that the LiNaSO₄ phase was formed on a surfaceof the LCO.

Evaluation Example 2: Lifespan Characteristics Evaluation

The lithium batteries prepared in Examples 1 to 4 and ComparativeExamples 1 and 2 were constant current/constant voltage charged with aconstant current at a rate of 0.1 C until a voltage was 4.5 V (vs. Li),and discharged with a constant current at a rate of 0.1 C until avoltage was 3 V (vs. Li) at 25° C. (A formation process)

The lithium batteries after the formation process were constantcurrent/constant voltage charged with a constant current at a rate of 1C until a voltage was 4.5 V (vs. Li), and discharged with a constantcurrent at a rate of 1 C until a voltage was 3 V (vs. Li) at 25° C. Suchcharging/discharging characteristic test was performed up to the 50^(th)cycle.

Capacity retention ratios (CRRs) of the lithium batteries prepared inExamples 1 to 4 and Comparative Examples 1 and 2 are shown in FIG. 3.The CRR is defined as shown in Equation 1.

CRR[%]=[Discharge capacity at each cycle/discharge capacity at 1^(st)cycle]×100

As shown in FIG. 3, the LCO coated with LiNaSO₄ (Examples 1 to 4)exhibited an improved capacity retention ratio per cycle in general,compared to the LCO that was not coated with LiNaSO₄ (ComparativeExample 1). In addition, in the case where a coating amount of LiNaSO₄was low (Comparative Example 2), the capacity retention ratio may alsolow.

As described above, according to one or more embodiments, the positiveactive material providing improved lifespan characteristics of a lithiumbattery may be obtained by coating or blending the positive activematerial with LiNaSO₄.

By way of summation and review, as a positive active material for thelithium secondary battery, a single-component lithium cobalt oxide(LiCoO₂) has been mainly used. Studies on improvement of LiCoO₂performance and development of an alternative material such as a3-component-based material or an olivine-based material have beenactively conducted due to capacity limitation and safety issuesregarding LiCoO2.

In particular, a 3-component-based lithium metal oxide,Li(Ni_(x)Co_(y)Mn_(1−x−y))O₂, has combined advantages of the highcapacity of LiNiO₂, the stable electrochemical characteristics ofLiCoO₂, and the thermal stability of Mn in LiMnO₂, and thus exhibitsexcellent electrochemical properties while having a relatively low cost.

However, with the 3-component-based material with high capacity, a largeamount of lithium may be deintercalated during a charging process andthus, the 3-component-based material may have an unstable structure.Capacity deterioration may occur after charging and discharging. Also,the 3-component-based material may have issues of thermal stability dueto a reaction with an electrolyte solution, and thus improvements inthese regards are desirable. A positive active material that improveselectrochemical characteristics of a lithium secondary battery byblocking a reaction between the positive active material and theelectrolyte solution during charging/discharging cycles of lithium isdesirable.

Embodiments provide a a positive active material that improves lifespancharacteristics of a lithium battery. Embodiments further provide alithium battery including the positive active material and a method ofmanufacturing the positive active material. A positive active materialmay improve lifespan characteristics of a lithium battery by including acoating of LiNaSO₄ on a surface of a core that includes a compoundcapable of reversibly intercalating and deintercalating lithium or byblending the core with LiNaSO₄.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope thereof as set forth in thefollowing claims.

What is claimed is:
 1. A positive active material, comprising: a coreincluding a compound capable of reversibly intercalating anddeintercalating lithium; and LiNaSO₄ that is coated on at least a partof a surface of the core or that blends with the core.
 2. The positiveactive material as claimed in claim 1, wherein the LiNaSO₄ is attachedon the core in a layered form or an island form.
 3. The positive activematerial as claimed in claim 1, wherein: an amount of the core is in arange of about 95 wt % to about 99.5 wt % of a total weight of the coreand the LiNaSO₄, and an amount of the LiNaSO₄ is in a range of about 0.5wt % to about 5 wt % of the total weight of the core and the LiNaSO₄. 4.The positive active material as claimed in claim 1, wherein: an amountof the core is in a range of about 97 wt % to about 99.3 wt % of a totalweight of the core and the LiNaSO₄, and an amount of the LiNaSO₄ is in arange of about 0.7 wt % to about 3 wt % of the total weight of the coreand the LiNaSO₄.
 5. The positive active material as claimed in claim 1,wherein the core includes at least one selected from compoundsrepresented by Formulae 1 to 3:Li_(a)(Ni_(x)M′_(y))O₂   [Formula 1] wherein, in Formula 1, M′ is atleast one element selected from Co, Mn, Fe, V, Cu, Cr, Al, Mg, and Ti;and 0.9<a≦1.1, 0≦x<0.4, 0.6≦y≦1, and x+y=1,LiMPO₄   [Formula 2] wherein, in Formula 2, M is at least one elementselected from Fe, Mn, Ni, Co, and V,Li_(1+y)Mn_(2−y−z)M_(z)O_(4−x)Q_(x)   [Formula 3] wherein, in Formula 3,M is at least one element selected from Mg, Al, Ni, Co, Fe, Cr, Cu, B,Ca, Nb, Mo, Sr, Sb, W, B, Ti, V, Zr, and Zn; Q is at least one elementselected from N. F, S, and Cl; and 0≦x≦1, 0≦y≦0.34, and 0≦z≦1.
 6. Thepositive active material as claimed in claim 5, wherein: the coreincludes the compound represented by Formula 1, and the compoundrepresented by Formula 1 is further substituted or doped with at leastone element selected from Ca, Mg, Al, Ti, Sr, Fe, Co, Cu, Zn, Y, Zr, Nb,and B, wherein the substituted or doped element is different from Ni andM′.
 7. A lithium battery, comprising: a positive electrode including thepositive active material as claimed in claim 1; a negative electrodefacing the positive electrode; and an electrolyte between the positiveelectrode and the negative electrode.
 8. The lithium battery as claimedin claim 7, wherein the lithium battery operates within a voltage rangeof about 4.3 V to about 4.6 V.
 9. A method of manufacturing a positiveactive material, the method comprising: preparing a compound capable ofreversibly intercalating and deintercalating lithium; adding and mixinga sodium source and a sulfate source to the compound to obtain a powdermixture; and heat-treating the powder mixture to obtain a positiveactive material including LiNaSO₄ that is coated on at least a part of asurface of the compound capable of reversibly intercalating anddeintercalating lithium or that blends with the compound capable ofreversibly intercalating and deintercalating lithium.
 10. The method asclaimed in claim 9, wherein the sodium source includes at least oneselected from sodium dodecyl sulfate (CH₃(CH₂)₁₁SO₄Na), sodium sulfate(Na₂SO₄), sodium nitrate (NaNO₃), sodium acetate (CH₃COONa), sodiumcarbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃), and sodium hydroxide(NaOH).
 11. The method as claimed in claim 9, wherein the sulfate sourceincludes at least one selected from sodium dodecyl sulfate(CH₃(CH₂)₁₁SO₄Na), sodium sulfate (Na₂SO₄), sulfuric acid (H₂SO₄),ammonium sulfate ((NH₄)₂SO₄), and lithium sulfate (Li₂SO₄).
 12. Themethod as claimed in claim 9, wherein the heat-treating is performed ata temperature in a range of about 600° C. to about 1,000° C.
 13. Themethod as claimed in claim 9, wherein: an amount of the compound capableof intercalating and deintercalating lithium is in a range of about 95wt % to about 99.5 wt % of a total weight of the compound capable ofintercalating and deintercalating lithium and the LiNaSO₄, and an amountof the LiNaSO₄ is in a range of about 0.5 wt % to about 5 wt % of thetotal weight of the compound capable of intercalating anddeintercalating lithium and the LiNaSO₄.